United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-074 May 1984
oEPA Project Summary
OHMSETT Test Series 77:
Global Oil Recovery Skimmer,
Veegarm Skimming Arm, Kebab
600, Wylie Skimmer, and the
Skim-Pak Cluster
Michael Borst
A series of tests was performed at the
Oil and Hazardous Materials Simulated
Environmental Test Tank (OHMSETT) to
provide information about the current
state-of-the-art in oil spill response
equipment. Funds were provided by the
OHMSETT Interagency Technical Com-
mittee (OITC) to test three advancing
skimmers (the GLOBAL oil recovery
skimmer (GORS),* the Veegarm sweep-
ing arm, and the Wylie skimmer) and
two stationary skimmers (the Kebab 700
and the Skim-Pak cluster).
The Hydrovac Veegarm and Kebab 600
are effective in the situations for which
they were designed. The Skim-Pak
cluster is somewhat of an improvement
over the basic device. The GORS shows
attractive potential for at-sea separation
Of collected oil and water, although the
proposed improvements tested here
were unsuccessful. The Wylie skimmer
failed to collect oil in all but the mildest
test environments.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The OHMSET Test Series 77 was funded
by the OITC. Members of this group include
* Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.
the U.S. Coast Guard, the U.S. Minerals
Management Service, Environmental
Canada, the U.S. Environmental Protection
Agency, and the U.S. Navy. Each of these
agencies has an interest in the oil spill equip-
ment and annually sponsors testing at
OHMSETT. All are committed to maintain-
ing an active knowledge of the current state-
of-the-art in oil spill response equipment. To
make effective use of funds, to ensure the
widest possible distribution of information
obtained, and to avoid costly repetition of
testing, these member agencies pooled their
resources and experience for testing three
advancing and two stationary skimmers dur-
ing the 1980 OHMSETT test season. The
three advancing skimmers chosen for testing
were the GORS, the Veegarm sweeping
arm, and the Wylie skimmer. The stationary
skimmers were the Kebab 600 (a rotating
disc device) and the Skim-Pak cluster (a
floating-weir skimmer).
The GORS is a modification of the DiPerna
skimmer, which had been tested at
OHMSETT previously. The external head
had been removed, and a floating weir was
substituted. Three rows of angle iron had
been welded across the bow of the skimmer
to dissipate waves before they contacted the
weir.
The Veegarm is a rigid boom skimmer in
commercial use around the world. The skim-
ming arm is the only part of the skimming
system tested.
The Wylie skimmer is a prototype skim-
mer designed for use with a boom rigged in
a catenary configuration. An extended, free-
floating head is intended to remove thick-
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ened oil from behind the apex of the boom.
The Wylie skimmer is built around an open-
ended vertical tank for oil-water separation.
The Kebab 600 is a stationary disc skim-
mer. A set of four rotating oleophilic discs
collect oil that has already been contained.
The device is intended for use when low-
water-content oil recovery is critical and
when the spill has been brought under
control.
The Skim-Pak cluster extends the concept
of the Skim-Pak skimming system previously
tested at OHMSETT. Rather than a single
skimming head-pump combination, six
heads are coupled to a common manifold to
scale up the oil recovery rate of the unit
without significant reduction in recovery ef-
ficiency.
Small Business Program
Three of the devices tested — the Kebab
600, the Wylie skimmer, and the Skim-Pak
cluster -- were chosen for study as part of
the small business program sponsored by the
OITC in November and December 1980. This
3-week program was aimed at small busi-
nesses and individuals who for economic
reasons could not otherwise test at
OHMSETT. The small business test pro-
grams was publicized in several trade jour-
nals and newsletters. Those interested in the
program were invited to apply for part of the
test time available. The OITC screened the
responses and selected three for testing
based on promise and innovation.
The participants were responsible for the
costs of shipping their devices to and from
OHMSETT and for the costs incurred by
their on-site technical consultants, which the
OITC required. All other costs for testing
were paid by the OITC. This program and
others like it provide useful information to
both the businesses and the OITC. The
private individuals receive the benefit of
OHMSETT's years of experience in addition
to the quantified performance testing. They
also receive practical information on the
state-of-the-art, recommendations of the
staff, and perhaps most important, an op-
portunity to observe their equipment at
work. The OITC receives an appraisal of the
current state of development work in the
private sector both from the equipment
tested and from the many imaginative
designs not selected for testing.
GLOBAL Oil Recovery Skimmer
The GORS is a modified version of the
DiPerna skimmer tested at OHMSETT in
1979. The GORS was tested to determine
the effectiveness of the modifications to the
DiPerna skimmer. Most modifications in-
volved the oil-collecting mouth of the device.
The vacuum head of the DiPerna Sweeper
was removed, and a floating weir was in-
stalled as a replacement. Three staggered
rows of 51-mm angle iron were welded ver-
tically across the bow of the skimmer to
dissipate the waves before reaching the weir.
The GORS uses a 6.3 m3 holding chamber
maintained at slightly less than atmospheric
pressure to draw oil over the weir. The
chamber is baffled and serves essentially as
a gravity oil/water separator. The heavier,
water-rich layer is pumped from the bottom
of the chamber to reduce the internal
pressures and draw additional fluid over the
weir. The floating, oil-rich layer is pumped
from the top of the holding chamber to a
more permanent storage area or the con-
tainer is used as temporary storage until the
skimmer can be unloaded.
The results of the 43 pre-modification and
38 post-modification tests indicate that the
principle behind the skimmer is sound. The
results also indicate that the modifications
were detrimental to the overall performance
of the skimmer. In almost all cases where the
test conditions were repeated, the perfor-
mance deteriorated. This was especially true
of the wave-dissipating angle-irons, which
tended to concentrate the wave energy and
entrain oil rather than dissipate the wave
energy.
Mechanical problems plagued the test
series. These were generally the result of
poor engineering, or maintenance, or both:
1. The free-floating weir did not have the
center of buoyancy and center of grav-
ity in the same vertical plane, which
caused the weir to twist and jam when
rising or falling. The tests were run with
a man constantly in position to free the
weir, but such a solution would be
unrealistic for spills in the real world.
2. The GORS came equipped with six on-
board pumps. The two single-
diaphragm pumps that were intended to
unload the oil-rich phase could not over-
come a 4-m head. This head could
easily be encountered when unloading
into barges at sea, so the pump system
is simply underdesigned.
3. Two centrifugal pumps intended to
unload the water-rich phase had been
exposed to the elements for too long
without routine, scheduled mainte-
nance. Much valuable test time was lost
in coaxing these pumps to work. Even-
tually, an OHMSETT positive displace-
ment pump was used to pump through
one of the onboard centrifugals.
4. The theoretical waterline should have
been calculated and the play of the weir
designed accordingly.
These problems are minor and can be
easily remedied with minimal investment of
time, money, and effort. They are not
detrimental to the concept of at-sea separa-
tion of collected oil and water, and they
should be considered as flaws in concept im-
plementation rather than as flaws of the con-
cept itself. The limited accessibility of storage
barges and tugs at a spill makes the concept
attractive.
The Hydrovac Veegarm
The Veegarm is a rigid-boom oil skimmer
produced and marketed by Hydrovac
Systems BV of the Netherlands. A rigid arm
channels the floating oil slick to a simple
overflow weir. The collected fluids are then
pumped to a large vessel that serves as an
oil-water separator.
The Veegarm was tow-tested at speeds
through 3 knots in calm water and wave con-
ditions. Two oils of very different viscosity
were used as test fluids in varying thick-
nesses. Fifty-six tests were performed on the
skimmer over 10 test days.
The Veegarm was well designed with
regard to strength, flotation, and stability.
The truss that supports the oil diversion
screen is constructed of rectangular steel
tubing and will withstand massive forces
before permanent deformation occurs. The
modular design allows for easy over-the-road
transportation and relatively simple air
shipment.
The largest wave the Veegarm was tested
in was a 0.63-m harbor chop — the only
wave in which the outboard pontoon left the
water surface. Although the Veegarm suf-
fered from occasional splashover, the bot-
tom of the screen was never exposed for
direct oil loss beneath it. A slick of contained
oil does form, and the headwave remains
parallel to the face of the skimmer. The
thickened layer of oil presented no real prob-
lems along the length of the screen, but the
headwave was entrained into the water at
the weir assembly at higher speeds.
Vortices that form at the ends of the weir
draw some oil into the water column. The
inboard vortex was of little consequence
because it seldom captured oil. The outboard
vortex captured more oil, but the total quan-
tity was small compared with the total
distributed and with losses from other failure
mechanisms. Losses occur between the
Veegarm and the support vessel hull. The
slick lost at this location is generally very
thick. When thick slicks are encountered in
calm water, the percentage of total loss is
significant.
The screen of the arm reflects incident
waves, which strike the next incident waves
and form a harbor chop. This effect is
especially evident when the waves are short
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and the arm is unable to respond to changes
in the water surface level. The wave reflec-
tions are of little significance in long waves.
Wylie Skimmer
The Wylie skimmer is constructed of spare
parts with minimal capital investment. The
skimmer is primarily a wooden structure that
uses 208-L drums for flotation. The device
successfully withstood 2-knot runs without
mishap. The device was designed around a
road-legal trailer and was sufficiently mobile
to be towed cross-country from British Col-
umbia to New Jersey. The unit is designed
to be a floating barge with an interior holding
tank for preliminary oil/water separation.
The tank is rectangular and has an open top
and bottom. The collected fluid is intended
to be of very high water content with free
water separation. An electric trolling motor
was used as a low-pressure pump to
minimize the mixing of oil and water.
The skimmer is designed to collect oil trap-
ped by a boom. The fluid passes from the
water surface to the separation tank through
a 203-mm stove pipe and flexible hose net-
work that will induce a counterclockwise cur-
rent in the separation tank. The intake to the
pipe-hose network was simply a length of
stove pipe mounted on a semicircular
wooden float.
The device was unable to collect oil from
the water surface under most conditions.
Because of the OHM SETT modifications, it
did collect minimal amounts of oil, but the
as-built model was incapable of collection in
anything but the mildest of test conditions.
The wooden float that supported the suc-
tion hose formed a clear water area compris-
ing 60% to 70% of the available oil-collecting
area at the pipe. If a means of oil removal
from the water surface is developed, the
skimmer will be limited to the working speed
of booms in a catenary configuration. Three
different mounting systems for the floating
intake were used.
Tests were run during which the separa-
tion tank was precharged with approximately
1 m3 of oil. These were run to find the max-
imum towing speed of the device when
operating if it were not boom-limited. At 1.5
knots, a large flow of oil was drawn from the
separation tank. The out-the-bottom loss
diminished as the tow speed decreased to
the critical speed of about 1 knot. These tests
were run with no attempt at further collec-
tion. The device losses through this
mechanism increase when additional oil col-
lection is attempted. Losses *rere apparent
at 0.25 knot with additional collection.
Kebab 600
The Kebab 600 is the smallest of a family
of disk skimmers marketed by Vikoma Inter-
national Ltd. The unit tested came with two
options: a 72-L floating reservoir and a small
hand pump. The Kebab 600 weighs 12 kg
and could have been positioned by a single
operator. The housing is constructed of
marine-grade aluminum that encloses five
stainless steel disks 278 mm in diameter. The
rotating disks are wiped by Teflon (PTFE)
scrapers. The collected oil runs into a trough
for removal. The disks are driven by a
variable-speed, 24-watt DC motor. The unit
tested functioned throughout the test period
without mechanical problems. The marine
design was adequate for the only wave used
in testing (0.19 m). The test unit was pro-
vided by Strauss Engineering, Mason, New
Hampshire.
The Kebab 600 could be used for oil spills,
but it is restricted by the designed low
recovery rate, and it would only be used to
its fullest capacity in small, contained spills.
A better application for a skimmer of this size
and capacity could be water effluent quality
control. Obvious examples of this type of ap-
plication include removing oil from gravity-
type separators or lagoon settling ponds.
The Kebab 600 can operate without per-
sonnel in attendance if a nonmanually-
operated pump is used. An electric pump in
a timed servo-cycle or a sensing probe of
some sort would work well if a more readily
usable holding reservoir were established.
Continuous pumping or simple gravity
overflow are simple solutions for industrial
applications, but they do not lend themselves
to spills.
The common trough may be placed in one
of two positions, depending on whether the
collected oil is to be pumped or gravity
discharged. When in the pumping position,
the wipers are not long enough to scrape the
entire surface of the disk. The outside sur-
face of the disk on each end is not scraped.
Both of these problems should be remedied.
Though wave testing was not as complete
as calm-water testing, the wave tests
generally produced equal or better values for
the oil recovery rate (ORR) and slightly lower
recovery efficiency (RE) values. When the
Kebab 600 faces oncoming waves, the col-
lection trough acts much like a weir.
The minimal storage capacity of the
floating reservoir is self-defeating. If the con-
cept of local storage is continued, reservoir
stability must be addressed. The reservoir
was not useful during the tests.
The hand pump does not supply the
necessary head for pumping high-viscosity
oil, but is able to pump water the required
height.
ORR increases with disk speed. Appar-
ently, a minimum of about 20 rpm is
necessary for effective collection in light oil.
The ORR is higher in heavy oil than in light,
but the RE is better in light. The Kebab 600
develops sufficient surface current to draw
nearby oil to itself.
Skim-Pak Cluster
The Skim-Pak skimming weir was tested
at OHMSETT in 1978 under OITC sponsor-
ship. These tests led to minor modifications
in the skimming head. The skimming heads
in the cluster were constructed of molded
fiberglass. Each head is rectangular, with
two tines straddling a self-adjusting flap,
which serves as a weir. The flap is intended
to allow high-oil-content fluid to be collected.
The skimmed oil is transferred through a
38-mm diameter hose 3 m long. These hoses
are jointed at a common cylindrical manifold
approximately 1 m in diameter and 0.25 m
high. A 76-mm diameter PVC hose connec-
tion is located at the center of the bottom
of the manifold for discharge. The unit tested
was a prototype developed and provided by
Douglas Engineering of Concord, California.
The Skim-Pak cluster produces a higher
ORR than a single skimming head, but not
in proportion to the number of heads.
The 1978 test program showed that the
skimming heads are much more effective
when attended with a control wand than
when free floating. These tests show similar
results when compared on a per-head basis.
The RE cannot be maintained, since the
multiple heads cannot be tended as the
single head can. Wave conformance was ex-
cellent. No diving or porpoising was ob-
served in the waves tested. A clear-water
problem did occur, however. The yawing of
individual heads created oil-free patches on
the water surface.
Inclement weather conditions hampered
the testing. Only 13 tests were conducted
over the 4-day period. Ice formation within
the manifold proved to be a severe problem.
This ice could not be freed by simply alter-
nating the flow direction from the pump.
The assembled cluster was difficult to
maneuver, and the required facilities could
not be available on boats for at-sea deploy-
ment. The fragility of the unit and the multi-
ple hoses would prevent throwing the cluster
over board for deployment. Field deployment
would probably require a man to be at the
water level or physically in the water.
Conclusions
Tests of the GORS showed that most
modifications of the original DiPerna skim-
mer were detrimental to the overall perfor-
mance of the device. The principle behind
the GORS was sound, however.
The Veegarm skimmer was well designed
with regard to strength, flotation, and stabil-
ity, but significant oil losses occurred bet-
3
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ween the skimmer and the support vessel
hull in calm water.
The as-built model of the Wylie skimmer
collected no oil in any but the mildest test
conditions. OHMSETT modifications pro-
duced little improvement in this skimmer's
performance.
The Kebab 600 could be used for oil spills,
but it is restricted by the designed low
recovery rate, and it would only be used to
fullest capacity in a small, contained spill.
Perhaps a better application for this size
skimmer would be water effluent quality
control.
The Skim-Pak cluster produces a higher
ORR than a single skimming head, but this
improvement is not in proportion to the
number of heads. Difficulties were en-
countered in maneuvering the assembled
cluster and in deploying it without special
facilities that would not be available at sea.
The full report was submitted in fulfillment
of Contract No. 68-03-3056 by Mason &
Hanger-Silas Mason, Inc., under the spon-
sorship of the U.S. Environmental Protec-
tion Agency.
Michael Borst is with Mason & Hanger-Silas Mason Co., Inc., Leonardo, NJ
07737.
Richard A. Griffiths is the EPA Project Officer (see below).
The complete report, entitled "OHMSETT Test Series 77: Global Oil Recovery
Skimmer, Veegarm Skimming Arm, Kebab 600, Wylie Skimmer, and the Skim-
Pak Cluster," (Order No. PB 84-168 293; Cost: $13.00. subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
US GOVERNMENT PRINTING OFFICE; 1984 — 759-015/7694
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
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